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tuj 03-08-2005 07:55 PM

braking technique
 
This is my first ABS car (I had a 96 Miata before) and after autocrossing my 8 for the first time last weekend, I am curious as to which is a better technique for hard braking in autox.

-hard application that triggers the ABS.

-threshold braking just below the point of ABS

Any opinions? Obviously not getting into the ABS is smoother, but in terms of overall stopping power, I was hard-pressed to really tell a difference between the two. My primary test was coming out of a fast straight at about 80 and having to brake hard for a 90 degree narrow left. I felt like I couldn't get to the edge of lockup and stay there without falling over into the ABS, unlike I could with my Miata.

Zaku-8 03-08-2005 08:07 PM

I'm curious, what is the reason not to trigger ABS? It's not like DSC where the computer holds throttle and interferes during a turn. It's just like if you were able to pump brakes with superhuman speed.

SDB 03-08-2005 09:05 PM


Originally Posted by Zaku-8
I'm curious, what is the reason not to trigger ABS? It's not like DSC where the computer holds throttle and interferes during a turn. It's just like if you were able to pump brakes with superhuman speed.

Actually it should be even better. It would require 4 brake pedals since ABS only pulses on the offending wheel or wheels. Only ABS can decide which wheel to pulse selectively, unless of course you do have the 4 brake pedal mod and have 4 feet.

tuj 03-08-2005 09:52 PM


I'm curious, what is the reason not to trigger ABS?
Well technically the ABS is pulsing the brakes, so there are moments when the brakes are not working as effectively as they could. If you were perfect, you could threshold brake, ie brake just up to the point where the wheel would lock, but not quite go over. This should be the maximum possible braking of the car. Of course, the problem with this is that its pretty hard to do in cars without ABS.

I feel like the ABS cuts in a bit early. Almost like it starts working when it detects a wheel slowing faster than it should be, cutting in before the threshold is reached. My question is, for those with more track and autox experience than myself, in places where hard braking is needed, is it more effective to try to brake as close to triggering the ABS as possible, or just mash the pedal and let the ABS work for you?

ZoomZoomH 03-08-2005 10:06 PM

i don't consider myself a great autoxer/track star (far from it :p ), but think of it this way: when your wheel locks up, it means you have overloaded the tire(s)' traction. All ABS/EBD do for you is it greatly reduces your chance of overloading the tires by intentionally *reduce* your braking power (aka the pulsing) so your tires have a chance to regain traction. If I was you, I'd think of ways to brake as little as necessary in order to get through a corner carrying as much momentum as possible :D

bmc 03-08-2005 11:30 PM

ABS is not as good as non-abs for straight line breaking. If you want to stop "Right now" ABS isn't what you want.

However, slowing down via ABS is faster than slowing down via "just off of ABS".

Plus, "stand on breaks" is much easier to reproduce than "modulate at this point in the pedal travel." Remember, consistancy is very important.

Imp 03-09-2005 05:55 AM


Originally Posted by bmc
However, slowing down via ABS is faster than slowing down via "just off of ABS".

I agree with your other two points, but I don't totally agree with this one. ABS disengages the brakes. Anytime that happens, in theory, you're increasing your stopping distances. If you're right on threshohold of lockup, you're applying the maximum braking the car can take... any less and you'll stop in further distance. Any more, ABS kicks in, and again, further distance.

That said... how many people can actually work the brakes to 100% threshold in an auto-x environment, never mind daily driving. :)

--kC

bmc 03-09-2005 06:42 AM

ok, sure you are probably right, but consistancy of how a car breaks is far more important than the very small benifit you would get staying out of ABS.

John V 03-09-2005 08:13 AM

In theory it's possible to stop faster without ABS. In practice, if you're close enough to the threshold you're going to cross it eventually - and once one wheel locks braking distances will increase dramatically, never mind the loss of control.

I'll take the consistency of a good ABS system any day.

The system on the base 350Z is a different story.

dmp 03-09-2005 08:34 AM

The absolute fastest way to stop is to lock up all tires. That creates the most friction. ABS won't help you stop FASTER - just help you to be able to steer whilst heavy on the brake pedal.

Imp 03-09-2005 08:44 AM


Originally Posted by dmp
The absolute fastest way to stop is to lock up all tires. That creates the most friction. ABS won't help you stop FASTER - just help you to be able to steer whilst heavy on the brake pedal.

And expensive too! :lol: (Flat spotting).

Yeah, I know what you mean about the 350Z abs... ever been in a WRX? Worse!

The 8's brakes and brake system are 10x better than the Subarus (wayy too sensitive)

--kC

John V 03-09-2005 08:54 AM


Originally Posted by dmp
The absolute fastest way to stop is to lock up all tires. That creates the most friction. ABS won't help you stop FASTER - just help you to be able to steer whilst heavy on the brake pedal.

:eek: This is not true at all for pavement, macadam, or concrete. This is only true on surfaces like gravel.

The sliding friction of a tire is much lower than the kinetic friction, and that doesn't take into account the overheating that will happen when a tire is locked up.

dmp 03-09-2005 09:00 AM

It's true for 'most conditions'. (shrug). ABS isn't a way to stop your car quicker - again, it's purpose is to allow people who PANIC when emergency-braking, so they don't lose their ability to steer the car :)

John V 03-09-2005 09:02 AM


Originally Posted by dmp
It's true for 'most conditions'. (shrug). ABS isn't a way to stop your car quicker - again, it's purpose is to allow people who PANIC when emergency-braking, so they don't lose their ability to steer the car :)

No. It's not true for most conditions. Your information is just patently false.

The fastest way to stop is to brake each wheel to the threshold of lockup. This is impossible to do repeatedly. ABS is a good compromise.

Locking the wheels isn't even close to the fastest way to stop. I don't know where you got the idea that it was. :confused:

http://www.sportrider.com/ride/146_9510_rss/
http://www.msgroup.org/forums/mtt/to...p?TOPIC_ID=153

dmp 03-09-2005 09:02 AM

More info:

http://www.nhtsa.dot.gov/cars/proble...absbrakes.html

A relevant quote:

"Do cars with ABS stop more quickly than cars without? ABS is designed to help the driver maintain control of the vehicle during emergency braking situations, not make the car stop more quickly. ABS may shorten stopping distances on wet or slippery roads and many systems will shorten stopping distances on dry roads. On very soft surfaces, such as loose gravel or unpacked snow, an ABS system may actually lengthen stopping distances."

dmp 03-09-2005 09:10 AM


Originally Posted by SoloII///M
No. It's not true for most conditions. Your information is just patently false.

The fastest way to stop is to brake each wheel to the threshold of lockup. This is impossible to do repeatedly. ABS is a good compromise.

Locking the wheels isn't even close to the fastest way to stop. I don't know where you got the idea that it was. :confused:

http://www.sportrider.com/ride/146_9510_rss/
http://www.msgroup.org/forums/mtt/to...p?TOPIC_ID=153


You are giving motorcycle links? :)

John V 03-09-2005 09:11 AM


Originally Posted by dmp
More info:

http://www.nhtsa.dot.gov/cars/proble...absbrakes.html

A relevant quote:

"Do cars with ABS stop more quickly than cars without? ABS is designed to help the driver maintain control of the vehicle during emergency braking situations, not make the car stop more quickly. ABS may shorten stopping distances on wet or slippery roads and many systems will shorten stopping distances on dry roads. On very soft surfaces, such as loose gravel or unpacked snow, an ABS system may actually lengthen stopping distances."

TRUE.

But nowhere does it say that a locked tire stops faster, so I'm not sure why you used that quote as support for your argument that a locked tire stops faster, because it does not. ABS may lengthen stopping distances in theory because there are times at which the brakes are not being applied. Furthermore, ABS effectively applies and releases the brakes rapidly - the best way to stop is not to force the tires to do sudden things. The fastest way is to threshold brake. Unfortunately, we haven't figured out how to detect how much force it takes to keep a tire BARELY rolling, so ABS is our best option.

John V 03-09-2005 09:12 AM


Originally Posted by dmp
You are giving motorcycle links? :)

I ride, so I have more motorcycle links than I do car links. Motorcycle tires act the same as car tires. :)

More:

http://avstop.com/Stories/Tires.htm

Relevant quote:

In discussing braking and tire damage, something new pilots may not think about is how bad locking an aircraft's brakes is on stopping an aircraft. A locked, skidding wheel assembly is not efficient in stopping an aircraft. Properly applied rolling friction on a properly inflated tire is what stops a tire in the shortest distance.

dmp 03-09-2005 09:14 AM


Originally Posted by SoloII///M
I ride, so I have more motorcycle links than I do car links. Motorcycle tires act the same as car tires. :)



...but i've only seen ONE car do a 'stoppie' :D

I'm not sure where I got the idea about locking up the tires - but i'm looking for suppoting information.

dmp 03-09-2005 09:15 AM


Originally Posted by SoloII///M
TRUE.

But nowhere does it say that a locked tire stops faster, so I'm not sure why you used that quote as support for your argument that a locked tire stops faster, because it does not. ABS may lengthen stopping distances in theory because there are times at which the brakes are not being applied. Furthermore, ABS effectively applies and releases the brakes rapidly - the best way to stop is not to force the tires to do sudden things. The fastest way is to threshold brake. Unfortunately, we haven't figured out how to detect how much force it takes to keep a tire BARELY rolling, so ABS is our best option.



That quote was used to defend the 'other' half of my statement, re: the purpose for ABS in the first place = 'NOT to shorted stopping distance" = ABS won't make your car 'stop' in a shorter distance.

dmp 03-09-2005 09:17 AM

Here's one bike-related link - I wish the guy would go into detail:

http://www.msgroup.org/Contrary/NEG085.html


The motorcycle is using more potential friction than the car. The difference is the tires. The reason you need better tires on the motorcycle is that it will only stay upright while the wheels are spinning. Consequently, locking the wheels it not an option. Conversely, locking all four wheels on a car is the fastest way to stop it.

John V 03-09-2005 09:20 AM


Originally Posted by dmp
Here's one bike-related link - I wish the guy would go into detail:

http://www.msgroup.org/Contrary/NEG085.html

"Consider the source."

This guy has no idea what he's talking about.

Had to look back and check, but I never said ABS gives the shortest stopping distances. I said it gives the most CONSISTENT braking and is very close to the shortest distance in practice. Theory is just that - theory.

Of course, you can verify this for yourself. Find an abandoned section of road and do some tests with and without ABS. It'll become obvious which is the faster way to stop pretty quickly. ;)

John V 03-09-2005 09:22 AM

More:

http://ecom.toyota-gib.com/English/V...04%20Terms.htm

Brake Lockup – In braking, lockup describes the point at which a tyre starts to skid in an emergency stopping situation. A tyre’s maximum braking force is developed when it is on the verge of lock-up, so a car’s shortest stopping distances are produced when its front and rear tyres are held just short of lockup. Anti-lock brakes (ABS) prevent wheel lockup, giving the advantage of simultaneous steering and braking ability (a locked wheel cannot be steered).

ULLLOSE 03-09-2005 09:26 AM

So where does it say the fastest way to stop is locking up all four wheels? btw for the most part no stock production brake system will lock all four at the same time. Due to a nearly 70% front brake bias you will almost never see stock rear brakes lock up in the dry, only the front will do it. I guess you must think drifting is the faster way around the track too. :eek:

John V 03-09-2005 09:31 AM


Originally Posted by ULLLOSE
So where does it say the fastest way to stop is locking up all four wheels? btw for the most part no stock production brake system will lock all four at the same time. Due to a nearly 70% front brake bias you will almost never see stock rear brakes lock up in the dry, only the front will do it. I guess you must think drifting is the faster way around the track too. :eek:

I'm glad somebody else is with me on this.

ULLLOSE 03-09-2005 09:46 AM

Yeah this is just stupid.... Watch ANY type of racing and what do you ALWAYS see the guy who locks up his brake doing......Going right off the end of the track...The fastest way to stop, lock up the brakes and hit another car or a wall. :p

dmp 03-09-2005 10:01 AM


Originally Posted by SoloII///M
"Consider the source."

This guy has no idea what he's talking about.

Had to look back and check, but I never said ABS gives the shortest stopping distances. I said it gives the most CONSISTENT braking and is very close to the shortest distance in practice. Theory is just that - theory.

Of course, you can verify this for yourself. Find an abandoned section of road and do some tests with and without ABS. It'll become obvious which is the faster way to stop pretty quickly. ;)



Follow me here:

I didn't indicate you indicated ABS gives the shortest stoping distance... :)


I'm saying "ABS won't make your car stop quicker". Then I stated "If you want your car to stop in the shortest distance, lock up all four wheels." I still think I believe that last statement, but I'm having trouble proving it.

:D

dmp 03-09-2005 10:02 AM


Originally Posted by ULLLOSE
Yeah this is just stupid.... Watch ANY type of racing and what do you ALWAYS see the guy who locks up his brake doing......Going right off the end of the track...The fastest way to stop, lock up the brakes and hit another car or a wall. :p


Nobody slides off the end of the track on a straight.... ;) We're discussing straight-line stopping.

John V 03-09-2005 10:13 AM


Originally Posted by dmp
Nobody slides off the end of the track on a straight.... ;) We're discussing straight-line stopping.

LOL. What is the reason you apply the brakes? For a turn, of course. :D

Study the physics of static / sliding friction enough and you'll prove to yourself that the sliding tire has less friction.

dmp 03-09-2005 10:19 AM


Originally Posted by SoloII///M
LOL. What is the reason you apply the brakes? For a turn, of course. :D

Study the physics of static / sliding friction enough and you'll prove to yourself that the sliding tire has less friction.


Maybe YOU have to apply brakes before turning....I drive an RX8!

:p


:)

I'll research more...I still believe i'm right. :D

John V 03-09-2005 12:22 PM


Originally Posted by dmp
I'll research more...I still believe i'm right. :D

:rolleyes: The truth hurts sometimes. :D

dmp 03-09-2005 12:26 PM


Originally Posted by SoloII///M
:rolleyes: The truth hurts sometimes. :D


I'll let you know. :)

Imp 03-09-2005 12:39 PM


Originally Posted by dmp
I'll research more...I still believe i'm right. :D

Good luck with that. ;)

Imp 03-09-2005 02:27 PM

What aould it take for us to convince you that you may have been incorrect in your belief that a skidding tire will stop faster/in a shorter distance than a non-skidding one?

Here's two quick articles I have found.... I can find many more... just tell me what source you would beleive if I found it, or could get a hold of it... if you don't believe these two....

Exhibit A:
http://www.canadiandirect.com/Renderer.jhtml.88.html


Then, squeeze the pedal down to the point just before the tires begin to skid - right at the limit of the tires's traction or grip. Never forget that if you lock-up the brakes and begin to skid, you have lost all directional control of the car. No matter what you do with the steering wheel, the car will continue straight ahead. Plus, a skidding car takes more distance to stop.
Exhibit B:
http://www.waltersforensic.com/artic...n/vol2-no1.htm


Wheel Slip-Threshold Braking

Wheel slip (skidding) occurs when the tire breaks traction with the road surface. When this occurs, friction is reduced between the tires and the road.

Skidding results in longer stopping distances. For the shortest possible stopping distance, the friction must be kept at a maximum. This is accomplished by "threshold braking", when the tire develops maximum friction without wheel slip.

A tire that is skidding has exceeded the maximum available friction and cannot provide maximum braking or effective steering.
Trust us when we say, and we have racing expereince... a skidding tire on pavement does not stop faster than a tire that's being threshold braked.

On snow, gravel, where you might be thinking you read this... you CAN stop faster by skidding. What happens is the locked tires form a wedge of snow/dirt and break through the loose surface to the substrate where it's not as slippery... and the wedge adds a coefficient of friction to the stopping tire by it's increasing base size. So... the choice is yours. This isn't a pissing contest. We're not going to hold you accoutable for a misunderstanding. We've all been there at one point in time.

--kC

Omicron 03-09-2005 02:32 PM

That's enough of the pissing-contest folks. I've cleaned up the posts, but if it continues after this point I'll have to close this otherwise good thread and start handing out warnings. Let it go, please.

dmp 03-09-2005 02:45 PM


Originally Posted by Imp
What aould it take for us to convince you that you may have been incorrect in your belief that a skidding tire will stop faster/in a shorter distance than a non-skidding one?

Here's two quick articles I have found.... I can find many more... just tell me what source you would beleive if I found it, or could get a hold of it... if you don't believe these two....

Exhibit A:
http://www.canadiandirect.com/Renderer.jhtml.88.html



Exhibit B:
http://www.waltersforensic.com/artic...n/vol2-no1.htm



Trust us when we say, and we have racing expereince... a skidding tire on pavement does not stop faster than a tire that's being threshold braked.


I've never claimed it'd be impossible to be 'proven wrong' - I'm saying I'm not convinced I just made it up - I know I heard/read it from a reputable source...still looking :)



On snow, gravel, where you might be thinking you read this... you CAN stop faster by skidding. What happens is the locked tires form a wedge of snow/dirt and break through the loose surface to the substrate where it's not as slippery... and the wedge adds a coefficient of friction to the stopping tire by it's increasing base size. So... the choice is yours. This isn't a pissing contest. We're not going to hold you accoutable for a misunderstanding. We've all been there at one point in time.

--kC
That could be - I have no issue with you - I have issue with one individual here with a complex; who can't seem to debate or discuss without insults. Neither you or ///M are 'that' person, fwiw.

tuj 03-09-2005 04:24 PM

One of the reasons I posted this question was that in my mind, it seemed like using the ABS was a good idea, since its easy to use and be consistent. However, watching other drivers in cars that were ABS equipped, it did not seem like they were getting into the ABS.

Obviously in an autox you aren't trying to stop the car, just get it slower as quickly as possible. This is why I brought up the smoothness of not hitting ABS as opposed to using it. Is there a significant advantage to keeping the car's motion smooth? I would think so, but I would think that then the ideal technique would be to go hard into ABS, and then taper out of it and trail brake into the turn.

BTW, the 8's brakes / suspension-under-braking are outstanding. I was very impressed with the stopping distances I was able to achieve.

dmp 03-09-2005 04:33 PM

Information I found:

http://bimmer.roadfly.org/3series/me...w35/26310.html

Your message says: "ABS puts the tires on the edge of lockup. That's as fast as your car will stop.".

Both parts of that sentance are flat out wrong.

First, ABS does not put the tires on the edge of lockup. ABS actually locks up the tires in small bursts. "Lock - off - lock -off" over and over again. It's not the edge of lockup, it's lockup and release, lockup and release, many times a second and much faster than a human driver.

The fastest way to stop a car is to lock up the wheels and skid to a stop. The only problem with doing so is you loose control of your car. Not a Good Thing. So ABS is one possible compromise: lock up your tires part of the time, but unlock them part of the time, so that you are able to steer your car in a full-braking situation. Another compromise is threshold braking - brake to the point that your wheels would lock, and not beyond.

Bigger rotors, nicer calipers, and etc will stop your car faster. If you've never experienced a brake conversion on a car, I guess I can't say anything to convince you otherwise. But nicer brakes will stop your car faster. Slotted rotors will allow for better disappation of heat, steam, and etc, which will allow for more consistent braking. Better gripping calipers or greater surface area on the rotors can cause the wheels to lock faster, and thus decrease braking distance. Better brakes can also allow you to threshold brake to a much higher degree, thus allowing for better braking.

Re-reading your message once again, I see that you could have been saying "ABS puts the car at the edge of lockup. And lockup is the fastest you can stop". If that's what you were trying to say, you didn't express yourself well :)
But to rebuke that, bigger brakes and better calipers will allow you to lockup your brakes faster than regular, which decreases brake time. Also, the better brakes allow for increased braking without lockup, good in real-world situations (outside of a 0-60-0 test that is).




Imp 03-09-2005 06:53 PM

Yeah, something like that posted in 2000 with no other "Googleable" sources... from an relative unknown... leads me to say one thing...

"I read it on a message board on the internet... it's got to be true." ;) (Then again, same thing could be said for this thread too... but I posted links to a couple reputable sources that weren't message forums.)

By the way... if you do want to believe that link... look at the big text on the top of the page.. that part that says "Actually, lockup isn't the fastest way to stop (m)" ..which was a one line answer to that comment. (All the italics on that page are quoting the message before it.) ;)

If lockup was the answer, tire companies would be even more rich from everyone flatspotting their tires from the skidding.

--kC

124Spider 03-09-2005 07:37 PM

I'm no expert, but, for autocross, I'm happy to engage ABS when I know that I'm going to be off the brakes before I turn the wheel, or expect to let up and do a bit of trail braking. It may be that an expert driver can slow down faster without ABS, but I can't, and one of the few things I've learned about autocross is that you want to be accelerating as much as possible in anything like a straight, so you will need to brake as you approach the sharp turns; you don't want to be braking hard in the turn, however. :eek:

Also, it's easier for me to heel/toe effectively if I'm braking hard than if I'm trying to carefully modulate my braking.

John V 03-10-2005 06:10 AM


Originally Posted by dmp

Oh man. :rolleyes:

There are many fallacies in that post. First of all, "Bigger rotors, nicer calipers, and etc will stop your car faster" is a big lie. Rotors, pads, calipers, the brake pedal, the master cylinder, the braided lines - NONE of this stuff stops the car. The TIRE stops the car, specifically the friction that exists between the tire and the road.

If your car is like most cars, then it has sufficient braking power from the factory to lock the tires if ABS is disengaged. Well if that's the case, how will bigger rotors, stiffer calipers, etc. stop the car faster? They can't. Not for one stop, at least. The exceptions are that they have decreased fade resistance so multiple stops in rapid succession may be shorter. They may have better modulation or bias.

Let's go back to the tire. The key point to debate in this scenario is whether a tire has the ability to generate more grip if it's sliding or static relative to the road. The answer is the tire should be static or nearly static relative to the road. i.e. at the threshold of lockup. ABS does not acheive this, but it's the best thing we've got.

JV

dmp 03-10-2005 09:08 AM

I think you've got me convinced, Solo. :)

John V 03-10-2005 09:25 AM


Originally Posted by dmp
I think you've got me convinced, Solo. :)

Sweet! Now, let's all have a group hug.

Oh yeah: buy my Hoosiers. ;)

:D

globi 03-10-2005 11:30 AM

I totally agree with what Solo II said:

Ideally you have to brake within a slip ratio of 2% to 20% (depending on the tire and surface conditions). The picture below shows a tire that reaches maximum braking performance (maximum friction coefficient) at about 18% slip ratio for a given surface:
http://www.whnet.com/4x4/pix/adhe.gif

The problem with ABS systems is that some of them reduce the brake pressure on the rear axle on purpose (so that the rear wheels won't lock at all), which makes the car more stable but also increases braking distance.

The DTM race cars use ABS and they wouldn't use it, if it wouldn't make the cars any faster.
http://www.dtm.de/

Matt RX8 03-15-2005 11:01 PM

I've only done 4 autocrosses (so take my advice with a grain of salt) but I've had some great training from a very good autocross driver.

I don't think there is a simple answer to your question. I think it depends on the course layout, the line you are taking, your driving skill, track conditions, etc... You'll have to judge each layout and probably experiment with both methods on any giving weekend to see what is the fastest way for you around the cones that day.

From my own experience, I was autoxing a newer BMW with ABS and recieving instruction from a guy with an older BMW without ABS. He had me going into full ABS lockup in some corners and trail braking through others. I would say that if you are going into a full braking situation that would otherwise lock up the tires, then you are better to use ABS as it will probably be smoother for you and you will lose less traction due to skidding tires. (think friction circle diagram)
Depending on the course layout, you might not do that really heavy braking very often. It would have to be a really tight hairpin for you to want to stop that completely. For sure use full ABS braking at the end of a run if you have a stopbox that you have to stop in.

I've never autoxed the RX8, but I would think brake less to carry speed through corners to compensate for lack of low end grunt. Torque shouldn't be a problem anyway as long as you keep the revs high. I'll be doing a ton of autocrosses in the 8 and a 2 day SCCA autocross shool next month. I'll let you know what I learn there.





Originally Posted by tuj
One of the reasons I posted this question was that in my mind, it seemed like using the ABS was a good idea, since its easy to use and be consistent. However, watching other drivers in cars that were ABS equipped, it did not seem like they were getting into the ABS.

Obviously in an autox you aren't trying to stop the car, just get it slower as quickly as possible. This is why I brought up the smoothness of not hitting ABS as opposed to using it. Is there a significant advantage to keeping the car's motion smooth? I would think so, but I would think that then the ideal technique would be to go hard into ABS, and then taper out of it and trail brake into the turn.

BTW, the 8's brakes / suspension-under-braking are outstanding. I was very impressed with the stopping distances I was able to achieve.


PedalFaster 03-20-2005 03:20 AM

I just read this thread for the first time, and now regret doing so -- I feel stupider for having done so. Hint: static versus dynamic coefficient of friction.

"It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt." - Mark Twain

tuj 03-20-2005 08:23 PM


Originally Posted by Machan
I've only done 4 autocrosses (so take my advice with a grain of salt) but I've had some great training from a very good autocross driver.

I don't think there is a simple answer to your question. I think it depends on the course layout, the line you are taking, your driving skill, track conditions, etc... You'll have to judge each layout and probably experiment with both methods on any giving weekend to see what is the fastest way for you around the cones that day.

From my own experience, I was autoxing a newer BMW with ABS and recieving instruction from a guy with an older BMW without ABS. He had me going into full ABS lockup in some corners and trail braking through others. I would say that if you are going into a full braking situation that would otherwise lock up the tires, then you are better to use ABS as it will probably be smoother for you and you will lose less traction due to skidding tires. (think friction circle diagram)
Depending on the course layout, you might not do that really heavy braking very often. It would have to be a really tight hairpin for you to want to stop that completely. For sure use full ABS braking at the end of a run if you have a stopbox that you have to stop in.

I've never autoxed the RX8, but I would think brake less to carry speed through corners to compensate for lack of low end grunt. Torque shouldn't be a problem anyway as long as you keep the revs high. I'll be doing a ton of autocrosses in the 8 and a 2 day SCCA autocross shool next month. I'll let you know what I learn there.

The course that caused to me post this thread was one that had me in third gear out of a straight into a 90 degree corner. Definetly was a hard braking situation. That course had several other places that went from fast to slow. The course today was totally different and I found myself doing pretty much only trail-braking. Today the problem was keeping speed up on the stock tires I've got without letting the rev's drop.

Which brings up another interesting question: how many people are left-foot braking? It seems like this would be an ideal car for that technique, just like the older rally cars with the laggy turbos. Guess I'll have to start learning.

John V 03-21-2005 05:14 AM


Originally Posted by tuj
Which brings up another interesting question: how many people are left-foot braking? It seems like this would be an ideal car for that technique, just like the older rally cars with the laggy turbos. Guess I'll have to start learning.

The rally cars LFB so they can keep the turbo spooled. Unless your RX-8 is turbocharged and you need to keep the engine on-boost, I wouldn't try it. I don't doubt it has the potential to be faster, but it is an awfully difficult technique to master.

JV


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